chore: explain what tests do

Author: Wybxc

tests/codegen/filename.rs

@@ -1,3 +1,5 @@
+//! Test that the generated code has the filename and function name in it
+
 // CHECK: filename
 
 #![feature(no_core)]

tests/codegen/params_count.rs

@@ -1,10 +1,13 @@
+//! Test that the generated code has the right number of parameters
+
 #![feature(no_core)]
 #![no_core]
 #![no_main]
 
 extern crate mini_core;
 
 // expect three int params
+// CHECK-LABEL: foo
 // CHECK: {{((int32_t .*,?\s?){3})}}
 #[no_mangle]
 pub fn foo(_x: i32, _y: i32, _z: i32) -> i32 {

tests/codegen/ret_value.rs

@@ -1,10 +1,11 @@
+//! Test that we can return a value from a function
 #![feature(no_core)]
 #![no_core]
 #![no_main]
 
 extern crate mini_core;
 
-// expect three int params
+// CHECK-LABEL: main
 // CHECK: 42
 #[no_mangle]
 pub fn main() -> i32 {